I put in the quick claw in case you wanted something other than bullet punch, i'd be willing to bet that a sudden hammer arm or zen headbutt would really irk someone's strategy. also you could breed your hydreigon with a gible or one of its evolutions and the Deino should know earth power upon hatching though that would mean training it from square one again, but thats what i did for my lv 88 salamence and garchomp and they just destroy the battle frontier on platinum(except when garchomp went up against a mamoswine and got hit with an avalanche)
also instead of a soft sand for your Gyarados you could give it an earth plate or a muscle band.

Excellent. But why Meteor Mash AND Bullet Punch? I read someone recommend a Zen Headbutt... Nahhh, too low accuracy for my taste and Psychic attacks have crappy coverage anyways. Any Steel type Lead (like Forretress for example) will laugh at this simply bc Meta wont be able to do a thing while Tress sets up their 3 layers of Spikes to truly damage ur team. This doesnt help a ton against forretress, but to aide you from getting walled by steels, ya might wanna consider EQ (which is fantastic anyways and covers most of what Bullet Punch doesnt, right???) And dont gotta worry about Flying leads, Aerodactyl being the most common whereas EQ stands no effect but BP will murder him in one hit.

Hydreigon! I love this thing! Coincidentally, I run the same moveset with mine. Tis great. Surf + Dragon Pulse gives you perfect coverage, then flamethrower to screw the steelys and Dark Pulse for some serious STAB with that beastly Sp.Atk. good thought with leftovers... But for his lack of pure speed being outsped by most dragons (EV trained for speed or not) you might wanna consider whatever berry it is that boosts speed... i forgot the name. lol

F&*K YEA RK Starmie! lol. Only change is take out TBolt for Grass Knot, cant let yourself get walled by those damned Perts, Quags, Carracosta and the other water/rock/ground vermin of pokemon... lol. And personally... I dont like Choice Items. Why not Life Orb? Provides a much better chance of doing a straight sweep of the team without having to switch on resistance right?

Ah... Standard DD Gyarados... What a beast... I hate these things. lol. Only change would beee.... Soft Sand? Might ask why? Perheps Leichi berry to raise attack that extra bit after 2 DD's for a succesful sweep? Dono. Ur choice. You could also make this Gyara a wall for your team, since your obviously set with plenty of sweepers. Gyara actually acts as a good wall, Intimidate crippling many leads, an to throw another wrench on it like I would, put Thunder Wave on him, just to piss ppl off. They wont expect it, and you can cripple their teams this way.

METAGROSS:
In the end, you're right. Earthquake > Meteor Mash. STAB is just soo attractive xD
Getting EQ would free me up to get another item, too :O Yeah, I think I'll do that.

HYDREIGON:
I don't think I'm terribly worried about speed... he'll outspeed what he outspeeds, and he'll take a hit when he can. His defenses are decent and the Leftovers provide a nice little boost. I like him :D

STARMIE:
I guess I just think Choice Items are cute. I don't like the recoil from Life Orb Dx
I guess for Starmie, though, Life Orb makes sense. It's still crippling in that I take recoil damage, but you have a good point about the sweeping potential.

GYARADOS:
I LOVE the sound of Thunder Wave! But what should I sub out? Ice Fang?
Anyway, I think I'm gonna go with Zanapher's suggestion and give him a Muscle Band instead of Soft Sand.

CHANDELURE:
You're right about the Psychic thing... but why would I put Grass Knot on him when he already has Energy Ball?
Maybe I should give him Will-O-Wisp. What's your opinion there?

and yea, TWave pisses ppl off anyways, but especially coming from a Gyarados (whom when you switch out you KNOW they will go for their best wall/sweeper crippler lol) and honestly, to really screw with ppl, id make that gyarados a tank. Swap ur EVs on Atk and Speed to Def and Sp Def, swap out Ice Fang for Avalanche, swap DD for TWave, Give em Leftovers and you have one meanass wall on your hands that can put out punishment when it needs to, take a crapload with his already great special defense (and intimidate makes up the other side of the spectrum) plus the EV spread I said, ull cripple/knock out their best pokes quite easily, and with surprise, bc EVERYONE and their mother wants to run Gyarados as DD sweeper.

and yea, TWave pisses ppl off anyways, but especially coming from a Gyarados (whom when you switch out you KNOW they will go for their best wall/sweeper crippler lol) and honestly, to really screw with ppl, id make that gyarados a tank. Swap ur EVs on Atk and Speed to Def and Sp Def, swap out Ice Fang for Avalanche, swap DD for TWave, Give em Leftovers and you have one meanass wall on your hands that can put out punishment when it needs to, take a crapload with his already great special defense (and intimidate makes up the other side of the spectrum) plus the EV spread I said, ull cripple/knock out their best pokes quite easily, and with surprise, bc EVERYONE and their mother wants to run Gyarados as DD sweeper.

Dahhh but I already EV-trained it ;-;

It's true that my team already has sweepers, though. Perhaps I'll get another one... it might be tedious, but I'm not in a rush or anything.

lol. well, thats just my take on it. i used Gyara as such before, and let me tell you... He was a pain in the ass for all that thought they could just come in and sweep with Mence or Garchomp, even Scizor couldnt do nothin... Hes like a sweeper killer.